Making Titles in 9.6.1 on a Mac

In iPhoto 9.6.1 you select a slide in your slideshow, then click the "Textslide" button. That will make a text overlay for the current slide. But you cannot customize the layout of the text, just enter the title text.

In the slideshow mode click on the Settings button at the bottom of the window. Then you can allow the photos title, description or both be displayed on the slide:

If you want to make your own slide you can use any image editor that can add text to a background or use Pages. With Pages select and 8 x 10 page size in landscape, create a black background (or any color you'd like) and add text to it in any font and style. The print the page to a PDF file. Open the file in Preview and export as a jpeg. Import that jpeg to your library and add to the slideshow.

Yes sorry. I thought you have been using using a saved slideshow project (with File > New Slideshow) all along. I never use the instant slideshows from an album. But you can open the slideshow settings even from an instant slideshow directly from an album, if you move the cursor into the playing slideshow to bring up the settings and then click the gears icon.

This will let you enable the titles as captions, if the theme permits it. And you can set this as a default.